1. Field of the Invention
The present invention relates to polymerizable organosilicon nanocapsules having a core and an organosilicon shell, processes for preparing, and uses of same. Such compounds are particularly suited for use in scratch-resistant coatings.
2. Discussion of the Background
It is known that the surface properties of sol or gel particles or of metal or semimetal oxides can be modified by treatment with a hydrolyzable organosilane or organosiloxane, which generally involves the attachment of just a single-ply silane layer to the oxide or sol gel particle. Oxides or sol or gel particles treated in this way, examples being inorganic pigments or fillers, may be incorporated into a polymer matrix, films, coating compositions and coatings producible therewith. In general, however, the scratch resistance of such polymer systems is low.
DE 198 46 660 discloses nanoscale, surface-modified oxide or mixed-oxide particles enveloped by organosilicon groups bonded covalently to the oxide particle, the organofunctional groups being described as reactive groups and normally being oriented outward, so that by means of polymerization they are bound into the polymer matrix with the polymer material when the prepolymer is cured. The process of preparing such coating compositions is complicated, since the organosilane and the oxide component are incorporated separately into the prepolymer.
DE 198 46 659 possesses the same priority as DE 198 46 660 and relates to a laminate provided with a scratch-resistant synthetic-resin layer which likewise contains nanoscale, surface-modified oxide particles. DE 198 46 659 teaches specifically the use of acryloyloxyalkylsilanes to produce a shell around nanoscale oxide particles that possess reactive, radiation-crosslinkable groups. The preparation of the coating composition in this case is likewise via a time-consuming reaction of a nanoscale silica with 3-methacryloyloxypropyltrimethoxysilane (DYNASYLAN® MEMO) in an acrylate formulation in the presence of water, an acid, and a wetting agent. Again, the components must be brought together separately and in a specific sequence.
Hydrolyzable silane components having ethylenically unsaturated organic groups are usually high-priced starting materials, however. In addition, DYNASYLAN® MEMO tends to react in the presence of even slight traces of a polymerization initiator or radiation with the undesirable result that the viscosity of a corresponding formulation may rise drastically. To avoid the unwanted polymerization, stabilizers must be added. It is therefore often difficult to master the handling of the starting materials and the preparation of such coating systems.
The coating compositions described above are frequently of high viscosity, and usually contain only a small fraction of oxide particles, which impacts the scratch resistance of the subsequent coating. It is difficult to apply such highly viscous coating compositions to a substrate, especially when the substrate in question is thin and can be destroyed by tearing. The scratch resistance of coatings obtainable in this way is in need of improvement, and with such highly viscous systems, a specific, complex application apparatus is required. In many cases, solvents are added to coating compositions of such high viscosity, but this undesirably leads to an increase in the organic emissions (VOC problem; VOC=volatile organic compounds).